U.S. patent application number 13/147785 was filed with the patent office on 2011-12-01 for process for recovering lignin.
Invention is credited to John C. Blackburn, Michael A. Lake.
Application Number | 20110294991 13/147785 |
Document ID | / |
Family ID | 43796458 |
Filed Date | 2011-12-01 |
United States Patent
Application |
20110294991 |
Kind Code |
A1 |
Lake; Michael A. ; et
al. |
December 1, 2011 |
PROCESS FOR RECOVERING LIGNIN
Abstract
There is provided a process for recovery of lignin from a black
liquor that contains either soluble or dispersed lignin, generating
a "liquid lignin" at high yield. Soluble lignin at elevated pH is
precipitated by reducing the pH of the black liquor stream by
countercurrent reaction with carbon dioxide, at elevated
temperature and pressure, creating two bulk fluid phases: a heavy
lignin-rich phase and a light lignin-depleted phase. The heavy
lignin-rich phase is separated and washed countercurrently with a
strong acid to displace metal cations from the lignin, creating a
low-salt lignin, which is then formed into a low-dust
high-bulk-density lignin fuel pellet. If needed, especially for
lignin recovered from kraft papermaking black-liquor streams, an
oxidation step is included to eliminate negative odor for
high-value green-chemistry applications.
Inventors: |
Lake; Michael A.; (Mt.
Pleasant, SC) ; Blackburn; John C.; (Charleston,
SC) |
Family ID: |
43796458 |
Appl. No.: |
13/147785 |
Filed: |
September 22, 2010 |
PCT Filed: |
September 22, 2010 |
PCT NO: |
PCT/US2010/049773 |
371 Date: |
August 3, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61245853 |
Sep 25, 2009 |
|
|
|
Current U.S.
Class: |
530/500 |
Current CPC
Class: |
D21C 11/0085 20130101;
C07G 1/00 20130101; D21C 11/0007 20130101; C08L 97/005 20130101;
C08H 8/00 20130101 |
Class at
Publication: |
530/500 |
International
Class: |
C08H 7/00 20110101
C08H007/00 |
Claims
1. A process for recovering lignin from papermaking black liquor
comprising: (a) carbonating said black liquor to neutralize NaOH
and other basic components contained therein; (b) recovering a
dense liquid-lignin phase; (c) acidifying said carbonated
liquid-lignin phase to neutralize residual NaOH and other basic
components, thereby generating an acidified dense lignin phase, (d)
recovering lignin from said acidified dense lignin phase; (e)
washing extraction of said acidified dense lignin phase to remove
residual acid and ash content, thereby generating purified lignin;
and (f) recovering said purified lignin.
2. The process according to claim 1 wherein said carbonation of
said black liquor is carried out by contacting said black liquor
with carbon dioxide countercurrently in an amount sufficient to
reduce the pH to less than 11, preferably a pH between 9.0 and
10.5.
3. The process according to claim 1 wherein said carbonating step
is carried out at a temperature between about 80.degree. C. and
200.degree. C., preferably a temperature between about 90.degree.
C. and 150 .degree. C.
4. The process according to claim 1 wherein an oxidizing agent is
reacted with said black liquor prior to carbonation in an amount
sufficient to eliminate or substantially reduce the odor of the
resulting lignin product.
5. The process according to claim 1 wherein an oxidizing agent is
reacted with said liquid-lignin phase in an amount sufficient to
eliminate or substantially reduce the odor of the resulting lignin
product.
6. The process according to claim 1 wherein said acidifying is
accomplished with a strong acid in an amount sufficient to reduce
the pH to less than 4, preferably a pH to between 1.5 and 3.5.
7. The process according to claim 1 wherein said acidifying
material is sulfuric acid.
8. The process according to claim 1 wherein said acidifying step is
carried out at a temperature up to 200.degree. C. to form a dense
liquid-lignin phase, preferably a temperature between about
80.degree. C. and about 150.degree. C., and most preferably a
temperature between about 100.degree. C. and about 130.degree.
C.
9. The process according to claim 1 wherein the vent gas generated
in step (c) is recycled to step (a).
10. The process according to claim 1 wherein said papermaking black
liquor is at a solids content between about 10% to about 70%,
preferably a solids content between about 30% to about 60%.
11. The process according to claim 1 wherein the black liquor feed
from a papermaking operation is removed downstream of a tall oil
soap separator.
12. The process according to claim 1 wherein said lignin product
from step (d) is shaped, including pelletizing.
13. A process for recovering lignin from kraft black liquor at a
solids content between about 30% and 60% comprising: (a)
carbonating said black liquor to neutralize NaOH and other basic
components contained therein at a temperature between 100.degree.
C. and 150.degree. C. in an amount sufficient to reduce the pH to
between 9 and 10.5; (b) recovering a dense liquid-lignin phase; (c)
acidifying said carbonated dense liquid-lignin phase with sulfuric
acid in an amount sufficient to reduce the pH to between 1.5 and
3.5 at a temperature between about 100.degree. C. and 130.degree.
C., thereby generating an acidified dense lignin phase, (d)
recovering lignin from said acidified dense lignin phase; (e)
washing extraction of said acidified dense lignin phase to remove
residual acid and ash content, thereby generating purified lignin;
and (f) recovering said purified lignin.
14. The process according to claim 13 wherein an oxidizing agent is
injected into said kraft black liquor prior to carbonation in an
amount sufficient to eliminate or substantially reduce the odor of
the resulting lignin product.
15. The process according to claim 13 wherein said lignin product
from step (d) is pelletized.
16. A process for recovering lignin from a crude lignin stream
within a biomass conversion process comprising: (a) carbonating
said black liquor to neutralize NaOH and other basic components
contained therein; (b) recovering a dense liquid-lignin phase; (c)
acidifying said carbonated liquid-lignin phase to neutralize
residual NaOH and other basic components, thereby generating an
acidified dense lignin phase, (d) recovering lignin from said
acidified dense lignin phase; (e) washing extraction of said
acidified dense lignin phase to remove residual acid and ash
content, thereby generating purified lignin; and (f) recovering
said purified lignin.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is, and Applicant claims the benefit of, a
national stage application filing under 35 U.S.C. 371 based on
PCT/US10/49773, filed Sep. 22, 2010, which claims the benefit of
priority from U.S. provisional application Ser. No. 61/245,853,
filed Sep. 25, 2009.
BACKGROUND OF THE INVENTION
[0002] (1) Field of the Invention
[0003] The present invention relates to processes for recovering
lignin from black liquor within a papermaking operation or a crude
lignin waste stream from a biomass enzymatic conversion process.
More particularly, the present invention relates to processes for
recovering and purifying lignin to produce a low-salt,
high-energy-content lignin fuel pellet.
[0004] (2) The Prior Art
[0005] Lignin, a component of wood, is the second most abundant
polymer in the world behind cellulose. Lignin is primarily
recovered from the black liquor stream within pulp and paper mills,
such as from the kraft pulping process. Black liquor is removed
from the host paper mill's recovery system downstream of an
efficiently-performing soap separator, since tall oil impurities
are deleterious to the operation of the unit operations of the
process and the downstream applications, especially the high-value
applications other than fuel pellets. Additionally, crude lignin is
a byproduct stream from the plethora of technologies using enzymes
being developed which convert the cellulose in biomass to ethanol
or other products. Those enzymes do not affect lignin which exits
those processes in various forms, generally low in solids and with
various pH depending on upstream treatments.
[0006] With its high energy density and variety of functional
groups and structure, lignin holds promise to be an efficient
biofuel source or green-chemical precursor. Thus, one use for
lignin is to recover lignin as a solid and burn the solid lignin as
a fuel, to or use the lignin as a binder for energy pellets.
Another use is to provide a process to recover a high-purity
low-salt lignin that is used to replace phenol used in resins for
composites, to be a natural polymer for making polyurethanes, or to
be used in a wide variety of alternative downstream chemical
applications.
[0007] Currently wood pellets are burned, but the ash content and
lower energy density limit their use as a fuel. Lignin pellets have
approximately the same energy content as coal, about 12,000 Btu/lb,
which is about 50% higher energy per mass of low-moisture wood
pellets having about 8,000 Btu/lb. Lignin pellets may be used alone
or blended directly with the coal feed with the only additional
capital being the separate storage and feeding equipment for the
pellets. Also lignin has demonstrated potential as an improved
binder for wood or grass pellets, decreasing the dust levels
generated in processing of the pellets, improving the water
resistance of pellets which is important for outside storage of
pellets, and increasing the energy density of the pellets.
[0008] Two lignin recovery methods from papermaking black liquor
are presently used. The first method, implemented in the 1940s
adjacent to a host kraft mill in Charleston S.C., makes powdered
lignin containing a high-salt content, which is difficult for power
companies to handle. The salt content also creates issues with high
ash within power furnaces. Also there is the problem of cooling and
diluting the black liquor that is returned to the host paper mills,
which creates a high energy penalty in the black liquor recovery
operation. The second method, in development since the 1990s, is
currently run as a demonstration plant in Sweden. This second
method makes low-salt lignin pellets used for fuel, but major
issues exist with high wash-water and energy penalty suffered by
the host paper mills. The filtrates from the second method have to
be returned to the host paper mill to recover the sodium but the
black liquor is cooled significantly (from >200.degree. F. to
<140.degree. F.) in addition to the wash water, which is
added.
[0009] Removing a fraction (up to 30%) of the lignin from black
liquor allows pulp and paper mills that have reached the maximum
throughput of their recovery boilers to increase production by the
same fraction of lignin removed. For example, a large paper mill
recovering 30% of their lignin from black liquor could produce
>50,000 tons of lignin pellets per year. If a papermaking
facility makes 50,000 ton/yr of lignin, and that lignin energy
value is replaced by burning residual wood, then that lignin is
used to displace coal, then the overall green-house gases are
reduced by 250,000 ton/yr.
[0010] Most pulp and paper mills have the infrastructure to gather
residual wood within an economically-effective radius (.about.70
miles) of the mill. Many of these mills have reached the limit of
their recovery furnaces because of heat-transfer limitations within
the furnace. The multiple tubes within the furnace that generate
steam on the inside with heat transferred from the burning
concentrated black liquor on the outside reach their upper limit of
heat flux. Increasing that heat flux risks catastrophic
consequences (recovery furnace explosions); thus mills don't exceed
that limit. Removing a fraction (.ltoreq.30%) of the lignin allows
the mills to increase their overall production rate of paper by
that same fraction.
[0011] Many states are implementing renewable energy thresholds on
electricity-generating power furnaces, many of which burn coal.
However, burning significant fractions of residual wood, as the
paper industry does, requires a different design of the furnace,
which would have a larger footprint and would require more capital
than a coal-burning furnace. A major factor is the lower energy
content of residual wood containing significant levels of water
(.gtoreq.40%); wet residual wood has as low as 25% the energy
density (Btu/lb) as coal or lignin pellets. To produce energy
pellets, the wood has to be dried to moisture contents of 10-20%,
but still the energy density of cellulose is still 2/3 that of
coal. And residual wood contains significant levels of inorganics,
which result in much higher levels of ash within the fuel, which
requires either specialized equipment to continuously remove the
ash or periodic shut-down to remove the ash. The paper industry
historically has build power furnaces capable of burning large
fractions of residual wood; the power industry has not. The power
industry can add small fractions of residual wood to their
furnaces, but a practical upper limit is soon reached. Additionally
the power industry and paper industry are frequently at odds,
competing for the same supply of residual wood.
SUMMARY OF THE INVENTION
[0012] In accordance with the present invention there are provided
processes for recovering lignin from black liquor to form a
liquid-lignin phase, purifying the lignin to requisite low-ash
levels, and producing a lignin particle Further, the process
provides for producing a lignin pellet to replace coal in existing
power furnaces. Alternatively, lignin in the form of
randomly-shaped particles exits one of the embodiments of the
process, saving the cost of extruder operation. The randomly-shaped
particles or pellets of lignin may be used as an improved binder
for the biomass-based energy pellet market.
[0013] Broadly speaking, the present invention provides processes
for recovering a liquid lignin from a lignin containing stream such
as a black liquor stream from a paper making process or the crude
lignin stream within an enzymatic biomass conversion process by
carbonating, acidifying and recovering the liquid lignin. More
specifically, the processes comprise as a first step, pressurizing
black liquor to between 50 and 200 psig. As an optional step,
sufficient oxygen may be reacted with the black liquor to reduce
and/or eliminate odors. The soluble lignin at a pH between 12 and
14 is precipitated by introducing the pressurized black liquor into
an absorption column and treating the black liquor, which is at an
elevated temperature and pressure, countercurrently with CO.sub.2,
to reduce the pH to between about 9 and 10 to partially neutralize
the NaOH and other basic components within the black liquor. The
carbon dioxide also converts much of the sodium (and other metals)
phenolic groups on the lignin molecules to the hydrogen form,
causing the lignin to become insoluble. The carbonated black liquor
and lignin undergo a phase separation creating a dense lignin-rich
"liquid lignin" phase and a light lignin-depleted phase. The light
lignin-depleted phase, being mostly black liquor, is returned to
the recovery process of the host paper mill at a temperature higher
than the temperature of the black liquor received, thus, removing a
major impediment for commercial implementation by paper mills.
[0014] The dense lignin-rich phase is washed countercurrently with
a strong acid, such as sulfuric acid to displace remaining sodium
ions from the lignin and further acidify the residual NaOH, other
basic components, and the residual NaHCO.sub.3 salt formed in the
carbonation column, creating a low-salt lignin at a pH less than 4.
The low-salt lignin is extracted or washed with water to remove the
residual acid and inorganic salts and then used as is or is
pelletized to form a low-dust, high-bulk-density lignin fuel.
[0015] An alternative is to take the dense liquid-lignin phase
directly into another pressurized reactor where the stream is mixed
with sulfuric acid. Depending on the nature of the lignin and the
temperature of the reactor, the lignin forms either another dense
liquid lignin phase or heavy solid granules that separate by
settling. Either of these lignin forms can be pumped or discharged
through a pressure-reducing valve into a countercurrent water
extraction system, where residual acid and salt are removed,
creating a low-ash lignin.
[0016] In either alternative, the off-gases from the acidification
reaction will be rich in CO.sub.2 from the reversal of the sodium
bicarbonate contained within the heavy liquid-lignin phase formed
in the carbonation system. Since this is a continuous process, this
CO.sub.2-rich vent stream can be recycled to the carbonation
system, reducing the overall process requirement of CO.sub.2.
[0017] Being a countercurrent continuous washing or extraction
system, the minimum levels of water will be required to achieve the
target ash level in the final product. Also a portion of the
extraction or wash water can be recycled to the acidification
reactor to reduce the process water requirements of the
process.
[0018] It is therefore the general object of the present invention
to provide a novel processes for recovering and purifying lignin to
produce a low-salt, high-energy-content lignin pellet, especially
useful as a fuel.
[0019] Another object of the present invention is to provide a
process that is suitable for high-value green-chemistry
applications such as replacing phenol in resins, providing a base
polymer for polyurethanes, and other end-use applications where the
chemical functionalities of lignin are employed.
[0020] Other object features and advantages of the invention will
be apparent to those skilled in the art from the following detailed
description taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Having described the invention in general terms, reference
will now be made to the accompanying drawings, which are not
necessarily drawn to scale, and wherein:
[0022] FIG. 1 is a schematic flow diagram which illustrates an
embodiment of the process of the present invention showing the
optional oxygenating step, the carbonating step, the acidifying
step and the extracting step;
[0023] FIG. 2 is a schematic diagram of an alternative embodiment
of the process of the present invention showing the application of
oxygenating after the carbonating step; and
[0024] FIG. 3 is a schematic diagram of an alternative embodiment
of the process of the present invention showing recycle of carbon
dioxide from the acidification settling tank to the carbonation
column.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0025] The present inventions now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather
these embodiments are provided so that this disclosure will be
through and complete and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to the
elements throughout.
[0026] Referring to FIG. 1, there is shown a schematic diagram of
an embodiment of a process of the present invention showing the
steps, from a lignin containing stream, of carbonating to form a
liquid-lignin, acidifying and recovering liquid-lignin. Black
liquor, leaving the soap separator in the pulp and paper plant, is
introduced through line 1 to pump A where the black liquor is
pressurized to between about 50 psig to about 200 psig, preferably
about 150 psig. Typically the black liquor is removed midway in the
evaporator train, is preferably at a solids content of 30% to 45%
and has a temperature of about 80.degree. C. to about 120.degree.
C. Keeping the heat of reaction in the pressurized system raises
the temperature significantly. It should be understood that the
solids content of the black liquor ranges from about 10% to about
70% but more normally is from 25% to 60%. The melt point of lignin
depends strongly on the level of sodium ions, the source of the
lignin, and the level of occluded black liquor in the lignin phase,
hence its viscosity is difficult to predict.
[0027] As an option, the pressurized black liquor may be reacted
with an oxidizing agent, such as oxygen, peroxide or the like, in
an amount sufficient to reduce or eliminate the odor level in the
black liquor so that there will be little or no odor in the final
lignin product. Only the odorous materials are intended to be
oxygenated, not the lignin material. This step removes the odor, by
reacting with the mercaptans (methyl, ethyl, dimethyl, and diethyl)
and other malodorous components. Preferred equipment for this
reaction is a Hydrodynamics Shockwave Power Reactor.RTM., shown at
B in FIG. 1. The oxygenation also has a substantial heat of
reaction, raising the temperature of the stream about 50.degree. C.
depending on the reactants within the aqueous stream and its solids
content. An alternative location in the process, that shown in FIG.
2, is to oxidize the liquid lignin exiting the carbonation column
C.sub.2 in line 6, and thereby conserving oxygen by not oxidizing
the entire black liquor flow. Another alternative is to not oxidize
the black liquor when applications are insensitive to the odor of
the final product, as typically would be the case when the lignin
is to be used as a fuel or as a binder for energy pellets.
[0028] Lignin begins to precipitate immediately near the black
liquor entrance near the top of the column as the pH begins to be
reduced by carbon dioxide. As the pH decreases from its high
(12-14) near the top to the exit at the bottom at pH 9-10, more and
more lignin becomes insoluble and coalesces within column.
Countercurrently contacting the incoming black liquor with
CO.sub.2, creates a pH gradient in a column so that liquid-lignin
droplets are created near the top that sweep and collect other
liquid-lignin droplets that are forming at the lower pH in the
lower zone of the column. The liquid-lignin particles have a
natural affinity for other liquid-lignin particles, facilitating
coalescence as they fall within the column. As the liquid-lignin
particles fall through the column, they collect other particles
that are forming at the lower pH within the lower zones of the
column. The dense particles then coalesce into a bulk liquid-lignin
phase which accumulates at the bottom of the column.
[0029] Pressurized black liquor is introduced via line 2 into the
top of a two part CO.sub.2 absorption column C. The size of the
column will depend upon the volume of black liquor being treated.
For example, in a column designed to process 50,000 tons of lignin
per year, the upper portion of the column C.sub.1 may be
approximately 6' diameter, 40' tall. The black liquor, with a high
NaOH content and a pH of near 14, reacts with the CO.sub.2 to form
NaHCO.sub.3. The column operates at a nominal pressure of 150 psig
and a temperature between about 80.degree. C. and 200.degree. C.,
preferably about 100.degree. C. to 150.degree. C. In the column,
the NaOH is neutralized, lowering the pH to less than pH 11,
preferably pH 9 to 10. This reaction causes the release of a
substantial exotherm, increasing the temperature of the stream
depending on the NaOH content and the solids level of the stream.
Malodorous gases leave the top of column C.sub.1 via line 4 and are
vented to the atmosphere. When the option of oxygenating is used,
the combined temperature rise of oxygenated and carbonated black
liquor is typically about 20.degree. C. or more.
[0030] The black liquor and lignin solution pass into the bottom
portion of the carbonation column C.sub.2, where the lignin
undergoes phase separation, forming a heavy liquid lignin phase.
The high temperature and pressure separation preserve heat from the
heats of reaction of the sequential reaction of O.sub.2, when the
oxygenating step is used, and CO.sub.2 that enables sending that
heat back to the recovery operation in the black liquor. The lower
portion C.sub.2 of the CO.sub.2 column is larger than the upper
portion. For example, the lower portion may be approximately 10' in
diameter and 15' tall for a 50,000 ton per year column. The carbon
dioxide also converts much of the sodium (and other metals) and
phenolic groups on the lignin molecules to the hydrogen form,
causing the lignin to become insoluble. The carbonated black liquor
and lignin undergo a phase separation creating a dense lignin-rich
"liquid lignin" phase and a light lignin-depleted phase. The black
liquor separates into the light (top) phase and is returned to the
recovery operation of the host paper mill via line 5. The dense
liquid-lignin phase leaves the bottom of the column C.sub.2 via
line 6.
[0031] A safety re-circulating loop is provided within column
C.sub.1 to remove excess heat if needed. The loop includes pump
D.sub.1 and heat exchanger E.sub.1. Alternatively, the temperature
within the column can be controlled with a heat exchanger on the
inlet black liquor line, controlling the temperature within the
column to provide optimum separation.
[0032] The lignin solution leaving the bottom of C.sub.2 via line 6
contains approximately 30-40% aqueous phase and goes to a
tangential entry cyclonic flash tank F. In the flash tank F, the
liquid-lignin solution is flashed down to atmospheric pressure with
the evolution of steam which is vented to the atmosphere through
line 8. Typically, about 85% of the aqueous phase is removed in
this step. The relatively dry lignin solution from flash tank F
passes through line 7 into an attrition unit G, such as a screw
conveyor, which pulverizes the lignin into a smaller size range.
The lignin particles are passed via line 9 to belt filter H. The
lignin particles remain large enough not to slow the filtration.
The belt filter H separates out any residual black liquor occluded
inside the lignin particles that was not previously removed. The
residual black liquor is returned to the pulp mill via a pump tank
I followed by intermittent service transfer pump J.
[0033] The lignin is then transferred via line 10, preferably by a
screw conveyor from the belt filter outfall to a mix tank K where
the lignin is washed with a strong acid, such as sulfuric acid, to
neutralize the residual NaOH. During this step the pH is reduced to
a pH less than 4, preferably from about 1.5 to about 3.5. An
agitator L provides a high level of mixing within a short residence
time. The acidified lignin slurry is then pumped M to drum filter
N, where the lignin is separated from the acid water, which is
removed through line 11. The acidifying step is carried out at a
temperature up to 200.degree. C. to form a dense liquid-lignin
phase. When the acidifying temperature is between about 90.degree.
C. and about 130.degree. C. lignin granules are formed. When the
acidifying step is carried out at a temperature above about
130.degree. C. a dense taffy-like lignin is formed. These
temperatures are dependent upon the specific nature of the
lignin.
[0034] Either of these lignin forms can be pumped or discharged
through a pressure-reducing valve into a countercurrent water
extraction system, where residual acid and salt are removed,
creating a low-ash lignin. For example, from the filter N, the
lignin filter cake is passed through line 12, preferably via a
screw conveyor to a second agitated mix tank O. Water is fed to the
mix tank via line 13 for thorough removal of sulfuric acid. A
centrifugal pump P is used to pump the wet lignin to another filter
Q, where it may be recovered and used as is.
[0035] Alternatively, the dried lignin is then conveyed through
line 14, preferably via a screw conveyor, to a pelletizer R, where
the lignin is pelletized. The pellets are then transferred to
pellet storage bin S using line 15. The dried lignin has an ash
content less than 1.0%, preferably less than 0.1%.
[0036] In an alternative of the processes of this invention, black
liquor is passed through line 2 to the two part absorption column C
where it is treated countercurrently with CO.sub.2 to lower the pH.
In the embodiment shown in FIG. 2 the liquid lignin leaves the
bottom portion C.sub.2 of the CO.sub.2 column through line 6 where
it is oxygenated. The oxygenated liquid-lignin phase is pumped
through line 10 into another pressurized mixer K where the stream
is mixed with sulfuric acid. Depending on the nature of the lignin
and the temperature of the reactor, the lignin forms either another
dense liquid-lignin phase or heavy solid granules that separate by
settling, such as in settling tank W. A stream of acid brine is
removed through line 16 and a stream of off-gases including
malodorous gases and carbon dioxide is removed through vent line
18. The dense liquid-lignin is passed through line 12 to an
extraction column T where water through line 13 is fed
countercurrently through the column. Being a countercurrent
continuous washing or extraction system, the minimum levels of
water will be required to achieve the target ash level in the final
product. Also a portion of the extraction or wash water can be
recycled to the acidification reactor to reduce the process water
requirements of the process. A low ash lignin is removed from the
bottom of the column and brine is removed from the top.
[0037] In FIG. 3 there is shown a variation of the processes shown
in FIG. 1 and FIG. 2. In either process, the off-gases from the
acidification reaction K will be rich in CO.sub.2 from the reversal
of the sodium bicarbonate contained within the heavy liquid-lignin
phase formed in the carbonation system. Since this is a continuous
process, this CO.sub.2-rich vent stream 18 can be recycled to the
carbonation column C, reducing the overall process requirement of
CO.sub.2. Additional CO.sub.2 is added through line 3.
Example 1
[0038] Black liquor was oxidized using the Shockwave Power Reactor
(SPR Hydrodynamics, Rome, Ga.). A single-pass and a two-pass
operation were run on each of the two kraft papermaking black
liquors. Data from the runs are shown in Table 1. The two-pass
oxidized black liquor samples were used for the following
examples.
TABLE-US-00001 Black Liquor A Black Liquor B at 38% solids at 48%
solids 1.sup.st Pass on 2.sup.nd Pass on 1.sup.st Pass on 2.sup.nd
Pass on SPR SPR SPR SPR Black Liquor Flow 1.8 1.8 2.2 2.2 (gpm)
Oxygen Flow (scfm) 3.0 2.7 4.0 3.8 T inlet .degree. C. 24 54 24 55
T outlet .degree. C. 93 75 98 99
[0039] Example 2
Carbonation Run at 150 C and 210 psig
[0040] A one-liter Parr reactor was charged with 1074 gram of black
liquor A having 37.3% solids. The black liquor was heated to
150.degree. C., introducing CO.sub.2 to raise the pressure to 210
psig. CO.sub.2 was allowed to enter the reactor through the sparger
to maintain the pressure until the reaction was complete. The
agitator speed was set at 60 rpm. A liquid-lignin phase was
collected from the bottom of the reactor; a clean, smooth interface
was observed for the interface, Analyses indicated that 37% of the
lignin in the black liquor had been precipitated. The solids
content of the liquid-lignin was 61%.
Example 3
Carbonation Run at 115 C. and 140 psig
[0041] The one-liter Parr reactor was charged with 979 grams of
Black Liquor A. The agitator was set at 60 rpm. The black liquor
was heated to 115.degree. C. and the pressure was maintained at 140
psig by the CO.sub.2. The reaction was allowed to continue to
completion, which was essentially complete after 75 minutes.
Liquid-lignin was collected from the bottom of the reactor; again a
clean interface was observed. Analyses indicate that 33% of the
lignin had been recovered in the liquid-lignin phase. The solids
content of the liquid-lignin was 61%.
Example 4
Carbonation at 150.degree. C. with High-Solids Black Liquor
[0042] A special two-liter reactor was fabricated with a 30-degree
conical bottom to allow better removal of dense phases. Into this
reactor, 2234 gram of Black Liquor B were charged having a solids
of 47.5%. The temperature was increased to 150.degree. C., and
CO.sub.2 pressure of 210 psig. The CO.sub.2 reaction was allowed to
continue to completion. Liquid-lignin was collected from the bottom
of the reactor; analyses indicate that 58% of the lignin had been
recovered. Samples of the liquid-lignin ranged from 60-70% solids.
These higher yields indicate the strong affect that black liquor
solids has on lignin recovery; the higher the black liquor solids,
the higher the recovery.
Example 5
Carbonation at 115.degree. C.; Acidification at Ambient
Temperature
[0043] A portion of the liquid-lignin from the carbonation at
115.degree. C. using Black Liquor A was allowed to cool at ambient
temperature and then ground into particles. 100 grams of these
particles were then mixed with 185 ml of 1N sulfuric acid,
sufficient to reduce the pH of the mixture to 3.4. The wet
particles were then separated by centrifugation, mixed with water
and centrifuged again. These wet particles were then mixed with
fresh water and centrifuged again. These wet particles were dried,
and the lignin weighed and analyzed. The ash level of the resultant
lignin was 0.7% of the sample, demonstrating the ash could be
washed effectively from the carbonated liquid lignin even at
ambient temperature.
[0044] Example 6
Carbonation and Acidification at 115.degree. C.
[0045] The two-liter reactor was charged with 1550 grams of Black
Liquor A. Agitation was set at 60 rpm, temperature was increased to
115.degree. C., and carbon dioxide was added to maintain pressure
of 210 psig for 42 minutes. Agitation was ceased and the reaction
mix was allowed to settle for one hour. The supernatant phase was
removed. The agitator was restarted at a rate of 180 rpm. The
carbonated liquid-lignin phase was acidified with 1N sulfuric acid
to a pH of 2.6. The acidified supernatant phase was collected, and
the acidified dense phase was removed and allowed to reach ambient
temperature. A portion of the dense phase was washed with water at
ambient temperature. The ash content of the final lignin product
was 3.5%.
[0046] Many modifications and other embodiments of the inventions
set forth herein will come to mind to one skilled in the art to
which these inventions pertain having the benefit of the teachings
presented in the foregoing descriptions. Therefore, it is to be
understood that the inventions are not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *